The present invention relates to a forming mold, more particularly to a shaping surface provided with a vent structure capable of efficiently releasing or removing air between the shaping surface and a material to be molded without producing unwanted protrusions such as spew and burr on the molded article.
In a forming mold for vulcanizing a rubber tire, curing a rubber article, injection molding or the like, if air remains between the shaping surface of the mold and the molded article, unwanted void or bareness of the material is formed in the molded surface. Therefore, various vent means are employed. For example, in case of a mold for curing a rubber article or vulcanizing a rubber tire, conventionally, vent holes and slit vents are used. In case of a mold for injection molding a golf ball, annular slit vent is employed.
The vent hole has a diameter of about 1 or 2 mm and formed in the shaping surface. Thus, the raw material (rubber) can easily flow out into the vent holes, and a number of spews are formed on the molded surface.
The slit vent is a narrow gap formed between metal parts of the mold. Thus, the formation of protrusions such as burr can be avoided. But, the position of the slit vent is very restricted and often combination use with vent holes is necessitated.